The present disclosure relates to image forming apparatuses such as copiers, printers, facsimile machines, and multifunction products having any of those integrated together. More particularly, the present disclosure relates to image forming apparatuses that use developer containing toner and magnetic carrier and that develop an electrostatic latent image on a photosensitive drum by making a developing roller carry toner alone.
As developing devices for developing an electrostatic latent image on a photosensitive drum as an image carrying member, there are known those adopting a single-component development method and those adopting a two-component development method. A two-component development method, for its use of developer containing toner and magnetic carrier, ensures a stable amount of electric charge for a long period and is thus suitable for aiming at a longer lifetime. For example, a developing device adopting a two-component development method accommodates developer containing toner and magnetic carrier, and feeds the developer from a stirring member to a developing roller. The developing roller includes a magnet inside it, and by the action of the magnet it carries the developer in the form of a magnetic brush on the surface of the developing roller. The developing roller, by rotating, transports the developer toward a photosensitive drum. The developing device further includes a restricting member for restricting the layer thickness of the developer with a view to making constant the amount of developer transported to the photosensitive drum by the rotation of the developing roller. Where the developing roller is located just opposite the photosensitive drum, only the toner contained in the developer carried on the developing roller is fed to the photosensitive drum, and an electrostatic latent image on the photosensitive drum is developed into a visible image in the form of a toner image.
When the restricting member restricts the layer thickness of the developer and forms a uniform layer of the developer on the surface of the developing roller, the toner in the developer is rubbed by the restricting member and scatters like a smoke of dust around the restricting member. The scattered toner attaches to and gradually deposits on the downstream-side surface of the restricting member with respect to the rotation direction of the developing roller. When the deposit of toner comes off the restricting member, is carried on the developing roller, and attaches to the photosensitive drum, it ends in being transferred onto a recording medium, producing a degraded image.
To prevent that, an image forming apparatus is so configured that, for the purpose of scraping off the deposit of toner attached to the restricting member, the rotation of the photosensitive drum is stopped with the developing bias between the photosensitive drum and the developing roller turned off, and moreover the developing roller is rotated in the direction reverse to that in which it is rotated during image formation.
There are various two-component development methods other than the one described above. For example, in one development method, toner alone is carried on the developing roller to develop an electrostatic latent image on the photosensitive drum. An image forming apparatus adopting this method includes a magnetic roller, a developing roller, and a restricting member. The magnetic roller, by action of a magnet included in it, carries developer containing toner and magnetic carrier in the form of a magnetic brush on its surface, and, by rotating, transports the carried magnetic brush. The developing roller is arranged opposite the image carrying member and opposite the magnetic roller, and carries on its surface the toner contained in the magnetic brush transported by the magnetic roller and feeds the carried toner to a photosensitive drum. The restricting member is arranged at a predetermined interval from the magnetic roller, and restricts the layer thickness of the developer on the surface of the magnetic roller. In this image forming apparatus, when toner is fed from the developing roller to the photosensitive drum to develop an electrostatic latent image on the photosensitive drum, the toner fed from the developing roller may, instead of being used in the development of the electrostatic latent image, scatter around the developing roller. The scattered toner falls onto the restricting member arranged opposite the magnetic roller. As image formation is repeated, the fallen toner deposits on the restricting member. During image formation, the deposited toner moves via the magnetic roller to the developing roller, and then attaches to the photosensitive drum. This, inconveniently, results in a degraded image on a recording medium.
The present disclosure is directed to an image forming apparatus that develops an electrostatic latent image on an image carrying member by making a developing roller carry toner alone, and aims to provide an image forming apparatus that collects toner that, instead of being fed to the image carrying member, has scattered around the developing roller.